Digital information is often transmitted via an air interface by modulating a high frequency carrier signal. The digital information is created and processed at a symbol rate, the symbol rate being determined by the time that is reserved to transmit a single symbol over the air interface. When different symbols are transmitted, a rather smooth transition between the subsequent symbols is created in order to avoid influencing neighboring channels and to not spoil the quality of the transmitted signal. When the transmitted digital information is represented by symbols within the complex plane, trajectories in the complex plane are created in between the consecutive symbols. The trajectories can thus be understood to be a representation of a complex valued signal generated by the transition between two subsequent symbols. The phase and the magnitude along the trajectories are modulated on the high frequency carrier in order to provide a smoothly varying modulated high frequency carrier. Depending on the modulator used, the modulation may be performed based on the magnitude parameter R and the phase parameter φ or on the real part (in phase component I) and the imaginary part (quadrature component Q) of the representation of the complex-valued signal defined by the trajectory in the imaginary plane.
It may be desirable to modify the characteristic of a complex-valued signal before modulating the high frequency carrier in order to avoid introducing distortions into the modulated signal.